Gene expression as a good indicator of aflatoxin contamination in dry-cured ham

Aspergillus flavus and Aspergillus parasiticus are mould species producers of aflatoxins (AFs) and may grow on dry-cured ham during the ripening process. In this study, the influence of different water activity (a_w) and temperatures on the temporal relative expression of three genes involved in AFs biosynthesis and their relationship with AFs production on dry-cured ham-based medium were evaluated. In general, the regulatory aflR and aflS genes showed similar expression patterns, and the expression of the structural aflP gene was much higher than that obtained for aflR and aflS genes. Regarding A. flavus, a decrease of a_w regardless of temperature caused an increase of the expression of the regulatory aflR and aflS genes. Concerning A. parasiticus, the highest and lowest expression values of the regulatory aflR and aflS genes were found at 0.95 a_w and 0.85 a_w, respectively. The expression of the structural aflP gene of both species was stimulated at low temperature and a_w. The PCA analysis indicated that both toxigenic species showed a strong correlation between the relative expression of the aflR and aflS genes and the concentration of AFs under conditions which simulate dry-cured ham ripening. This suggests that an early detection of the expression of regulatory genes can be a good indicator of possible AFs contamination of dry-cured ham through ripening.